<!DOCTYPE html>
<style>
    .block { width:50px; height:25px; break-inside:avoid; }
</style>
<p>There should be a hotpink square below.</p>
<div style="columns:3;">
    <div style="break-after:column;">
        <div class="block"></div>
        <div class="block" style="background:hotpink;"></div>
        <div class="block"></div>
        <div class="block"></div>
        <div class="block"></div>
    </div>
    <div style="column-span:all;"></div>
    <div class="block" style="background:hotpink;"></div>
</div>
